Solid Foods Up Baby's Obesity Risk

Introducing solid foods too early raises the risk of obesity. But breastfed and formula-fed babies are different.

Whether or not to breastfeed and at what point to introduce solid foods to baby are questions that have gotten a lot of attention in recent months. Some researchers argue that babies should be breastfed exclusively for the first six months of life and not be offered solid foods in this time. Other experts take issue with both of these recommendations. A new study adds fuel to the fire by showing that breastfeeding may have an important benefit over formula-feeding as solid foods are introduced: protection against obesity later on.

Babies who were formula-fed, which included babies who had never been breastfed and those who had switched from breast to formula before they were 4 months old, were six times as likely to become obese if they were given solids before 4 months of age.

The researchers behind the current study followed 847 babies for the first three years of life. They asked the mothers if and for how long they had breastfed their babies, or when they had switched to formula. They also looked at what age the babies had been introduced to solid foods. When the children were three years old, their body mass indices (BMIs) were calculated; those who fell into the top 5%, which was 75 of the children in the study, were considered obese.

For babies who had been breastfed, the timing of the introduction of solid foods did not matter. That is, whether babies were introduced to solids before 4 months, from 4-5 months, or at 6 months or later, had no effect on whether they would go on to be obese toddlers. But for babies who were formula-fed, which included babies who had never been breastfed and those who had switched from breast to formula before they were 4 months old, it was a different story. Babies in this group were six times as likely to become obese if they were given solids before 4 months of age. If they were started on solids between 4 and 5 months, their odds of becoming obese dropped to less than that of breastfed babies. If they were started on solids after 6 months, their obesity risk rose again, but there were too few babies in this group to draw any concrete conclusions.

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So why the difference between the breast and the bottle when it comes to weight gain? The researchers suggest that it may have to do with self-regulation. When solid foods are introduced, a baby’s energy intake increases slightly, so self-regulation becomes important. Breastfed babies – and their mothers – may be better able to tell when baby’s had enough, compared to formula-fed babies and their moms. Earlier studies have also shown that when solids are introduced before 6 months of age, breastfed babies "compensate" by drinking less milk, but formula-fed babies do not.

Childhood obesity is a growing epidemic in the U.S. The authors underline the fact that finding the earliest prevention strategies is key in fighting it, particularly since there may be a "critical window" for obesity risk in these first few months of life. They conclude that for babies who are predominantly formula-fed, waiting until after 4 months to begin solid foods is the best bet. Speak with your baby’s pediatrician if you have any concerns about the best choice for you and your baby.

The study was carried out by researchers at Children's Hospital Boston, and published in the February 7, 2011 issue of Pediatrics. It can be accessed here.